1. Field of the Invention
The present invention relates, in general, to the integration of a discrete semiconductor laser with a discrete monitoring photodetector (MPD), wherein light from the back facet of the semiconductor laser is guided to the MPD through a polymer light guide.
2. Description of the Background Art
Semiconductor lasers typically are fabricated by growing the appropriate layered semiconductor material on a substrate through Metalorganic Chemical Vapor Deposition (MOCVD) or Molecular Beam Epitaxy (MBE) to form an active layer parallel to the substrate surface. The material is then processed with a variety of semiconductor processing tools to produce a laser optical cavity incorporating the active layer, and metallic contacts are attached to the semiconductor material. Finally, laser mirror facets typically are formed at the ends of the laser cavity by cleaving the semiconductor material to define edges or ends of the laser optical cavity so that when a bias voltage is applied across the contacts the resulting current flow through the active layer causes photons to be emitted out of the faceted edges of the active layer in a direction perpendicular to the current flow.
The prior art discloses processes for forming the mirror facets of semiconductor lasers through etching, allowing lasers to be monolithically integrated with other photonic devices on the same substrate. The formation of total-internal-reflection facets within an optical cavity through the creation of such facets at angles greater than the critical angle for light propagating within the cavity is also known.
A new type of surface emitting semiconductor laser has been fabricated with etched mirrors or facets. This laser is known as a Horizontal Cavity Surface Emitting Laser (HCSEL) and is disclosed in US Patent Application Publication No. US 2005/0083982 A1, which was published Apr. 21, 2005 and in U.S. Pat. No. 7,245,645, issued Jul. 17, 2007, the disclosures of which is hereby incorporated herein by reference.
Packaging of a semiconductor edge-emitting laser (EEL) with an MPD requires the EEL to be mounted in a transistor outline package (TO) at an angle relative to the MPD, as shown in FIG. 1, which shows the inside of a TO can 10 with an EEL 12 and an MPD 14 mounted therein. In the illustration of FIG. 1, the EEL 12 is shown horizontally mounted on a submount 16. First, second and third TO can pins 18, 20 and 22 are provided which act as electrical connections to the EEL 12 and MPD 14. The MPD 14 is shown mounted vertically to the end of the center pin 20. A plurality of wirebonds 24 is provided to interconnect the EEL 12 and MPD 14 to the TO can pins 18 and 22 and to the can 10.
The rear facet of the EEL 12 is facing the MPD 14 so that the MPD 14 can monitor the light from that facet. Sometimes the MPD 14 is positioned slightly off from perpendicular to the incidence of the light beam from the rear facet to prevent back reflection into this facet. As illustrated, a three-dimensional packaging operation is thus required to form the package shown in FIG. 1, with chip mounting and wirebonding in two different planes of the package.